Design and performance of a double-solenoid magnetic bottle photoelectron spectrometer for attosecond metrology.

The design and performance of an in-house developed double-solenoid magnetic bottle (MB) time-of-flight photoelectron spectrograph are presented. A combination of a strong permanent magnet (Sm2Co17) with a soft iron cone and a double-solenoid geometry is used to generate MB configuration. The first solenoid (length ∼150 mm) is placed inside the vacuum, and the second solenoid (length ∼1 m) is placed outside the vacuum. The double-solenoid geometry improves the effective conductance and reduces overall material outgassing. Due to this, an ultra-high vacuum (∼5 × 10-8 mbar) desirable for the working of the spectrograph was achieved using a small capacity (300 lps) turbo-molecular pump. An optimization of solenoid current generates a smooth magnetic field variation in MB, which keeps the adiabaticity parameter ∼0.6 at ∼25 eV photoelectron energy. The double-solenoid geometry also provides high collection efficiency as well as high energy resolution of the spectrograph. The experimentally measured energy resolution (ΔE) of the spectrograph is better than ∼60 meV at ∼15 eV photoelectron energy. The collection efficiency is estimated to be ∼25% under optimum conditions as compared with ∼10-4 in field-free configuration. The calibrated MB spectrograph is used for the characterization of the attosecond pulse train using a cross-correlation "RABBITT" technique. The attosecond pulse train is generated from 15th to 25th odd high-harmonic orders, in argon filled cell. Attosecond pulses of average duration ∼260 as (FWHM) have been measured. The proposed MB electron spectrograph design provides a compact experimental setup for attosecond metrology and pump-probe studies with a relaxed requirement on vacuum pump capacity.

Effect of Ti: Sapphire and Nd: YAG Lasers on Shear Bond Strength at the Zirconia - Veneering Ceramic Juncture.

Introduction: This study was conducted to assess the impact of nanosecond and femtosecond lasers on shear bond strength at the zirconia - veneering ceramic juncture. Materials and Methods: The first 60 samples of partially sintered zirconia cylindrical discs measuring 7 mm diameter and 4 mm height were milled and sintered. Then they were randomly divided into three groups namely group C (control, n=10), group N (Nd: YAG laser, n=10), and group T (Ti: sapphire laser n=40) which was further divided based on the duration of laser irradiation, into 4 subgroups (n=10 each) which were 30 seconds, 1 minute, 2 minutes and 3 minutes. Surface treatment was done on sintered zirconia discs based on the group. Following the treatment, the discs were ultrasonically cleaned followed by liner application (IPS Emax Zirliner, Ivoclar-Vivadent) and veneer ceramic layering (IPS e.max Ceram, Ivoclar-Vivadent) of 1.5 mm height. Each sample underwent shear stress in the universal test machine on the mounting jig, and bond strength was evaluated. Data were assessed using ANOVA followed by Tukey's post hoc multiple comparison analyses. Results: According to one-way ANOVA, there was a significant difference in shear bond strength between the groups. Tukey's post hoc pair wise comparison test showed a significant difference (P value = 0.001) in shear bond strength of all pairs except group C and group N. The results of repeated measures, ANOVA (related and dependent groups) and Tukey's multiple pair wise comparison test showed that there was a significant difference (P value = 0.001) in shear bond strength at 30 seconds and all other groups. Conclusion: Ti: sapphire laser irradiation for 30 seconds can be used as potential surface treatment to increase shear bond strength at the zirconia-veneering ceramic juncture.

Refurbishment of an Au-coated toroidal mirror by capacitively coupled RF plasma discharge.

Deposition of synchrotron-radiation-induced carbon contamination on beamline optics causes their performance to deteriorate, especially near the carbon K edge. The photon flux losses due to carbon contamination have spurred researchers to search for a suitable decontamination technique to restore the optical surface and retain its performance. Several in situ and ex situ refurbishing strategies for beamline optics are still under development to solve this serious issue. In this work, the carbon contamination is removed from a large (340 mm × 60 mm) Au-coated toroidal mirror surface using a capacitively coupled low-pressure RF plasma. Before and after RF plasma cleaning, the mirror was characterized by Raman spectroscopy, soft X-ray reflectivity (SXR) and atomic force microscopy (AFM) techniques. The Raman spectra of the contaminated mirror clearly show the G (1575-1590 cm-1) and D (1362-1380 cm-1) bands of graphitic carbon. The SXR curve of the contaminated mirror shows a clear dip near the critical momentum transfer of carbon, indicating the presence of carbon contamination on the mirror surface. This dip disappears after removal of the contamination layer by RF plasma exposure. A decrease in the intensities of the CO bands is also observed by optical emission spectrometry during plasma exposure. The AFM and SXR results suggest that the root-mean-square (r.m.s.) roughness of the mirror surface does not increase after plasma exposure.

Micrometer-sized negative-ion accelerator based on ultrashort laser pulse interaction with transparent solids.

We report here energetic (>100 keV) negative hydrogen ions (H(-)) generated in the interaction of moderately intense (10(18) W cm(-2)) ultrashort laser pulses (45 fs) with transparent hydrogen containing solid targets. An unambiguous and consistent detection of negative hydrogen ions, with a flux of 8×10(11)H(-) ions/sr, has been observed in every single laser shot, using a Thomson parabola ion spectrograph. Simple estimates based on charge transfer cross sections match well with experimental observations. Our method offers the implementation of an intense, ultrashort laser based negative-ion source at a higher repetition rate, which can be important for various applications.

Role of target material in proton acceleration from thin foils irradiated by ultrashort laser pulses.

We report on the proton acceleration studies from thin metallic foils of varying atomic number (Z) and thicknesses, investigated using a 45 fs, 10 TW Ti:sapphire laser system. An optimum foil thickness was observed for efficient proton acceleration for our laser conditions, dictated by the laser ASE prepulse and hot electron propagation behavior inside the material. The hydrodynamic simulations for ASE prepulse support the experimental observation. The observed maximum proton energy at different thicknesses for a given element is in good agreement with the reported scaling laws. The results with foils of different atomic number Z suggest that a judicious choice of the foil material can enhance the proton acceleration efficiency, resulting into higher proton energy.

Analysis of higher harmonic contamination with a modified approach using a grating analyser.

Soft x-ray spectra of the toroidal grating monochromator (TGM) at the reflectivity beamline of Indus-1 synchrotron source are analyzed for higher harmonic contribution. A diffraction grating of central line spacing 1200 l/mm is used to disperse the monochromatic beam received from TGM to quantify the harmonic contents in the 50-360 Å wavelength range. In order to calculate the harmonic contamination, conventionally the intensity of higher order peak is divided by first order peak intensity of the desired wavelength. This approach is found to give wrong estimate as first order peak itself is overlapped by higher order peaks. In the present study, a modified approach has been proposed to calculate harmonic contamination where the intensity contributions of overlapping orders have been removed from the first order diffraction peak of the desired wavelength. It is found that the order contamination in the TGM spectra is less than 15% in the wavelength range of 90-180 Å. The total harmonic contribution increases from 6%-60% in the wavelength range of 150-260 Å. The critical wavelength of Indus-1 is 61 Å hence the harmonic contamination below 90 Å is significantly low. The results obtained with modified approach match well with those obtained by quantitative analysis of multilayer reflectivity data. The obtained higher harmonics data are used to fit the transmission of aluminum edge filter in the 120-360 Å wavelength range.

Efficient Kalpha x-ray source from submillijoule femtosecond laser pulses operated at kilohertz repetition rate.

We report an efficient Cu K(alpha) x-ray source produced by focusing submillijoule, 120 fs Ti:sapphire laser pulses on a solid copper target to a spot diameter of few microns. The experimental results show strong emission of K(alpha) x-rays from solid targets from microplasmas created by p-polarized 0.2-0.3 mJ laser pulses at 1 kHz repetition rate. We have demonstrated K(alpha) x-ray point source emission rates of 6.7 x 10(9) photonss into 2 pi sr at 1 kHz repetition rate. The source has an x-ray conversion efficiency into Cu K(alpha) line emission of 3.2 x 10(-5). The source has a measured size of approximately 8 microm. Such a high repetition rate K(alpha) x-ray source can be very useful for time resolved x-ray diffraction and radiographic applications.

Experimental study of harmonic generation from solid surfaces irradiated by multipicosecond laser pulses.

An experimental study is presented on harmonic generation from solid surfaces using 27 ps Nd:glass laser pulses (lambda=1053 nm) in the intensity range of 10(13)-10(15) W cm(-2). Second, third, and fourth harmonics emitted in the specular reflection direction showed intensity scaling exponents of 1.5, 1.8, and 3.8 for an obliquely incident p-polarized laser beam, providing a conversion efficiency of 2x10(-8), 10(-10), and 5x10(-12) at 10(15) W cm(-2), respectively. Second and third harmonic radiation generated using an s-polarized pump was about 10 and 100 times smaller, respectively, compared to that for the p-polarized laser radiation. Faraday rotation observed in the reflected fundamental radiation can explain the relative harmonic yields for the p and s polarizations of the pump beam.

Characterization of X-ray contact microscopic imaging in keV spectral region using laser produced plasmas.

An experimental study is performed of soft X-ray emission from laser produced plasmas for single shot X-ray contact microscopic imaging of physical and biological microstructures. Planar copper targets are irradiated by 10 J, 28 nS Nd:glass laser pulses in the intensity range of 1011 W/cm2 to 3 × 1012 W/cm2. Measurements of keV X-ray emission viz. X-ray intensity scaling with laser intensity, X-ray source size, X-ray conversion efficiency and exposure dose on the sample are presented. Fine copper grids of 70 mm mesh size and 10 mm thickness are used as test samples for imaging on ERP-40 photoresist. A spatial resolution of ~195 nm is observed, consistent with theoretical estimate considering the contribution of geometrical and diffraction blurring, and statistical noise of photons incident on the sample. This study should be useful in proper selection of source parameters for optimization of spatial resolution in single shot keV contact imaging.